This section introduces aspects that may help facilitate a better understanding of the disclosure. Accordingly, these statements are to be read in this light and are not to be understood as admissions about what is or is not prior art.
An optical wavelength division multiplexing (WDM) technique can be implemented in order to use a single fiber to carry multiple optical channels at different WDM wavelengths. In order to increase the number of optical WDM channels carried by a fiber within a given spectral bandwidth, the frequency spacing between two adjacent WDM wavelengths must be reduced. However, as this frequency spacing reduces, the frequency spacing must be tightly controlled so that undesirable optical cross talk is avoided. If different lasers are used to generate different optical WDM channels, the lasers have to be controlled to avoid frequency drifts and fluctuations in the lasers.
One approach is to use a single laser with a comb generator. A mode locked comb laser can be used to produce a frequency comb with a plurality of regularly spaced frequency modes. Lasers which serve to generate an optical comb for use in, e.g., WDM systems, are known in the art.
The Optical frequency comb generator developed based on the Kerr effect in nonlinear microresonators is an attractive comb generator for its simplicity, small size, and potential of chip-level integration. For many applications, the tunability of the generated combs is required to perform some essential functions, such as aligning the comb lines with the channels in optical WDM communication systems, or achieving stabilization guided by self-referencing with an f-2f interferometer. One method of tuning, namely simply adjusting the pump frequency and utilizing the thermal self-locking effect, has been demonstrated for a fused silica microresonator. But generally combs are not expected to maintain a uniform low-noise state in the tuning process, because the intensity noise and coherence of Kerr combs sensitively depend on the phase detuning between the resonance and the pump frequency.
Another challenge with such comb generators is that the excitation wavelength of the source laser has to be tuned to the resonator. Such tuning circuits are complex. Therefore, there is an unmet need for a comb generator capable of producing a plurality of wavelengths while maintaining a match between the laser source wavelength and the desired output wavelengths of the resonator in an effective but simple fashion.